Coast FIRE is the point where your invested assets are large enough to grow to your full retirement number on their own — no additional contributions required. Reaching it does not mean you retire today, but it does mean your future retirement is secured. Understanding this milestone and how to reach it faster is one of the most motivating frameworks in the FIRE movement.

What Coast FIRE Actually Means

Coast FIRE is a specific milestone within the broader Financial Independence, Retire Early (FIRE) framework. When you hit your Coast FIRE number, your current investment balance — left alone to compound at your expected real return — will grow to your full FIRE number by the time you reach your planned retirement age. The key phrase is "left alone": you do not need to add another dollar. You have effectively pre-funded your retirement and are just waiting for time and compound interest to complete the job. This is a powerful psychological shift. Before Coast FIRE, every month of not saving feels like falling behind. After Coast FIRE, you have optionality — you can continue saving aggressively to retire earlier, scale back to a less demanding job, switch careers entirely, or work part-time and cover only current expenses. The pressure of needing to save for the future evaporates. Unlike full FIRE, which requires enough saved to stop working immediately, Coast FIRE only requires enough invested today that your future self is financially secure regardless of what happens with your career or income from this point forward.

How the Coast FIRE Calculation Works

The calculation has two steps. First, determine your FIRE number: divide your expected annual retirement spending by your safe withdrawal rate (typically 4%). If you plan to spend $60,000 per year, your FIRE number is $1,500,000. Second, discount that FIRE number back to today's dollars using your real rate of return — the nominal return minus inflation, calculated precisely using the Fisher equation. If your real return is 3.88% (7% nominal, 3% inflation) and you have 28 years until retirement, your Coast FIRE number is $1,500,000 / (1.0388)^28, which is approximately $510,000. The real return is used instead of the nominal return because your spending target ($60,000) is stated in today's dollars. Using the real return ensures your projection accounts for inflation automatically. The sensitivity to each input is significant: a one-percentage-point decrease in your expected real return increases your Coast FIRE number substantially, so it is wise to check your result at multiple return assumptions rather than relying on a single optimistic projection.

The Role of the Safe Withdrawal Rate

Your safe withdrawal rate (SWR) is the percentage of your retirement portfolio you withdraw in the first year, with subsequent years adjusted for inflation. The 4% rule — drawn from the original Trinity Study — found that a 60/40 stock-bond portfolio could sustain 4% annual withdrawals for 30 years in virtually all historical market scenarios, including periods beginning just before major crashes. However, the 4% rule was designed for a 30-year retirement, not a 40 or 50-year one. If you plan to retire at 50, many financial planners recommend using 3.25–3.5% instead to account for the longer horizon and increased sequence-of-returns risk. A lower SWR increases your FIRE number and therefore your Coast FIRE number — for example, switching from 4% to 3.5% raises a $60,000-spending FIRE number from $1,500,000 to $1,714,000. When in doubt, use a conservative SWR for your Coast calculation and treat any shortfall from using the full 4% as a built-in safety margin, not a gap you must close.

Life After Coast FIRE

Reaching Coast FIRE opens doors that are closed when you are still in the accumulation phase. Many people use the milestone to transition from high-paying but stressful careers to work they find more meaningful, even at lower salaries. Since covering current expenses is all that is required — not building future retirement savings — a significant income reduction becomes sustainable. This pattern, sometimes called Barista FIRE or Semi-FIRE, allows people to step off the aggressive savings treadmill while their invested assets continue compounding in the background. Others use Coast FIRE as confirmation to accelerate: knowing the retirement floor is secured, they focus any additional savings on paying off a mortgage, funding a business, or building a taxable brokerage account for early retirement years. The psychological value of knowing your retirement is already locked in — regardless of what happens to your income — is hard to overstate. It changes how you negotiate salary, tolerate a difficult boss, and make career decisions, because your long-term financial security no longer depends on any single employer or income stream.